1. Field of the Invention
The present invention relates to pneumatic apparatus of the percussive type and more particularly to single-stroke pneumatic apparatus.
2. Description of the Prior Art
For marking, centre-pricking, marking-off and chiselling off risers use is commonly made of a single-acting pneumatic apparatus. The tool the apparatus is fitted with varies with the application. It can be a stamp, a prick-punch, a hobby or a chisel supported in a hollow frame with inlet and outlet ports and a striker dividing the bore of the frame into forward- and back-stroke chambers. A directional flow control is provided on the frame. The source of energy is compressed air fed from a mobile or stationary compressor over a flexible hose. In operation, the compressed air admitted into the chambers of the frame with the aid of the directional flow control maniplated by the operator, causes the striker to reciprocate back and forth axially and deliver cyclewise blows at the end face of the tool. The work done by the tool materializes in any of the following operations depending on tool type: marking, centre-pricking, chiselling or riveting.
The apparatus is a manually-operated one and must therefore be reliable in operation and create unstrained labour conditions. The degree of its engineering perfection is determined, among other things, by the apparatus capacity, i.e. by the energy of the blows.
Known in the art is a single-stroke pneumatic apparatus (cf. USSR Inventor's Certificate No. 706,239, IPC B25D 9/04, 1979) in the hollow cylindrical frame, of which there is located a tool at an end with provision for back and forth reciprocation of a striker with a tail piece and a callibrated orifice. The striker divides the bore of the frame into fore and back chambers communicating with each other by way of the calibrated orifice. A spring-loaded head with a tip in the form of a valve is provided at the forward end of the frame, and a cover is provided at the rear end of the frame.
The striker and its tail piece interacting with the cover of the frame and the calibrated orifice through which the fore and back chambers communicate are additional sources of friction which diminish the energy of blows. Some of the energy is also lost due to leaks of compressed air from the fore chamber into the back one during operation.
Also known is a single-stroke pneumatic apparatus (cf. USSR Inventor's Certificate No. 1,027,026, IPC B25 D 9/04, 1983) comprising a hollow cylindrical frame having a strating means, inlet and outlet ports overlapped in turn by a directional flow control sleeve. The frame contains a striker and has a tool mounted at the front end thereof. The striker divides the bore of the frame into fore and back chambers. The directional flow control sleeve has inlet passages in the form of longitudinal flats which hamper the high-velocity flow of compressed air into the fore chamber. The speed of the striker consequently decreases and so does the energy of the blow.
The starting means provided in the form of a valve which can be set open only by pressing the tool against the work strains the operator who starts the apparatus with effort.